Two-Part Plastic Retaining Ring

ABSTRACT

A retaining ring includes a generally annular lower portion and a generally annular upper portion. The lower portion has a bottom surface for contacting a polishing pad during polishing and a top surface. The upper portion has a bottom surface secured to the top surface of the lower portion and a top surface configured to be mechanically affixed to and abut a rigid base of a carrier head. The lower portion is a first plastic, and the upper portion is a different second plastic that is about the same or more rigid than the first plastic.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser. No. 61/515,814, filed on Aug. 5, 2011, the entire disclosure of which is incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to a retaining ring for a carrier head for chemical mechanical polishing.

BACKGROUND

Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of a patterned layer is exposed. A conductive filler layer, for example, can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative layer. After planarization, the portions of the conductive layer remaining between the raised pattern of the insulative layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness is left over the non-planar surface. In addition, planarization of the substrate surface is usually required for photolithography.

Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. A polishing liquid, such as a slurry with abrasive particles, is typically supplied to the surface of the polishing pad.

The substrate is typically retained below the carrier head by a retaining ring. However, because the retaining ring contacts the polishing pad, the retaining ring tends to wear away, and is occasionally replaced. Some retaining rings have an upper portion formed of metal and a lower portion formed of a wearable plastic, whereas some other retaining rings are a single plastic part.

SUMMARY

Retaining rings can be expensive, and as noted above, need to be periodically replaced when worn. The bottom of the retaining ring that contacts the polishing pad is formed of a plastic, but due to constraints, e.g., degree of rigidity, wear rate, chemical resistance, and the like needed for the bottom of the retaining ring, the selection of suitable plastic compositions is limited, and thus the plastic can be fairly expensive. A technique is to form both the upper and lower portion of the retaining ring from plastic, with the upper portion formed of a different plastic than the plastic of the lower portion. This may permit the upper portion of the retaining ring to be made from a low cost material.

In one aspect, a retaining ring includes a generally annular lower portion and a generally annular upper portion. The lower portion has a bottom surface for contacting a polishing pad during polishing and a top surface. The upper portion has a bottom surface secured to the top surface of the lower portion and a top surface configured to be mechanically affixed to and abut a rigid base of a carrier head. The lower portion is a first plastic, and the upper portion is a different second plastic that is about the same or more rigid than the first plastic.

Implementations may include one or more of the following features. The lower portion may be secured to the upper portion and the top surface may be configured such that the retaining ring is removable as a unit from the base so that the upper portion remains secured to the lower portion while the retaining ring is removed. The lower portion may lack any aperture from the top surface to the bottom surface of the lower portion. The lower portion may be attached to the upper portion by an adhesive, e.g., an epoxy. The lower portion may have a durometer measurement between about 80 and 95 on the Shore D scale. The upper portion may have a durometer measurement of at least 70 on the Shore D scale. The upper portion may have a greater elastic modulus than the lower portion. The lower portion may be thicker than the upper portion. The first plastic may be selected from the group consisting of polyphenylene sulfide (PPS), polyaryletherketone (PAEK), polyetheretherketone (PEEK) and polyetherketoneketone (PEKK). The second plastic may be selected from the group consisting of polyvinyl chloride (PVC), polypropylene (PP), polycarbonate (PC), polyaryletherketone (PAEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polybutylene terephthalate (PBT), polyoxymethylene (POM), polyethylene terephthalate (PET), perfluoroalkoxy (PFA), polyamideimide (PM) or polytetrafluoroethylene (PTFE). The bottom surface of the lower portion may have channels for slurry transport. The retaining ring may have an inner side wall and an outer side wall, and the inner side wall and outer side wall may be oriented vertically from the top surface of the upper portion to the bottom surface of the lower portion. The inner surface and the outer surface of the lower portion and upper portion may be flush where the lower portion and upper portion are joined. The top surface of the upper portion may include a hole to receive a fastener to mechanically affix the retaining ring to the base.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of a carrier head.

FIG. 2A is a side view of a retaining ring.

FIG. 2B is a bottom view of the retaining ring.

FIG. 2C is a cross-sectional view of the retaining ring.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

During a polishing operation, one or more substrates can be polished by a chemical mechanical polishing (CMP) apparatus that includes a carrier head 100. A description of a CMP apparatus can be found in U.S. Pat. No. 5,738,574.

Referring to FIG. 1, an exemplary simplified carrier head 100 includes a housing 102, a flexible membrane 104 that provides a mounting surface for the substrate, a pressurizable chamber 106 between the membrane 104 and the housing 102, and a retaining ring 110 secured near the edge of the housing 102 to hold the substrate below membrane 104. Although FIG. 1 illustrates the membrane 104 as clamped between the retaining ring 110 and the base 102, one or more other parts, e.g., clamp rings, could be used to hold the membrane 104. A drive shaft 120 can be provided to rotate and/or translate the carrier head across a polishing pad. A pump may be fluidly connected to the chamber 106 though a passage 108 in the housing to control the pressure in the chamber 106 and thus the downward pressure of the flexible membrane 104 on the substrate. The retaining ring 110 may be a generally annular ring secured at the outer edge of the base 102, e.g., by screws or bolts 136 that extend through passages 138 in the base 102 into aligned threaded receiving recesses 139 (see FIG. 2C, which illustrates one recess) in the upper surface 112 of the retaining ring 110. In some implementations, the drive shaft 120 can be raised and lowered to control the pressure of a bottom surface 114 of the retaining ring 110 on a polishing pad. Alternatively, the retaining ring 110 can be movable relative to the base 120 and the carrier head 100 can include an internal chamber which can be pressurized to control a downward pressure on the retaining ring, e.g., as described in U.S. Pat. Nos. 6,183,354 or 7,575,504, which are incorporated by reference. A distinguishing feature of a retaining ring is that it is removable from the base 102 (and the rest of the carrier head) as a unit. In the case of the retaining ring 110, this means that an upper portion 142 of the retaining ring 110 remains secured to a lower portion 140 of the retaining ring while the retaining ring 110 is removed, without requiring disassembly of the base 102 or removal of the base 102 from the carrier head 100.

An inner surface 116 of retaining ring 110 defines, in conjunction with the lower surface of the flexible membrane 104, a substrate receiving recess. The retaining ring 110 prevents the substrate from escaping the substrate receiving recess.

The bottom surface 114 of the retaining ring 110 can be substantially flat, or as shown in FIGS. 2A and 2B, in some implementations it may have a plurality of channels 130 that extend from the inner surface 116 to the outer surface 118 of the retaining ring to facilitate the transport of slurry from outside the retaining ring to the substrate. The channels 130 can be evenly spaced around the retaining ring. In some implementations, each channel 130 can be offset at an angle, e.g., 45°, relative to the radius passing through the channel. The channels can have a width of about 0.125 inches. In some implementations, the channels are flared at the outer surface of the retaining ring.

Referring to FIGS. 2A and 2C, the retaining ring 110 includes multiple vertically stacked sections, including the annular lower portion 140 having the bottom surface 114 that may contact the polishing pad, and the annular upper portion 142 connected to base 104. The lower portion 140 can be bonded to the upper portion 142 with an adhesive layer 144.

The lower portion 140 is a first plastic, e.g., polyphenol sulfide (PPS), whereas the upper portion 142 of retaining ring 110 is a different second plastic, e.g., polyvinyl chloride (PVC), polypropylene (PP), or polycarbonate (PC). The first plastic has about the same rigidity as the second plastic, or the first plastic is a more rigid material (i.e., has a higher elastic modulus) than the second plastic.

The plastic of the lower portion 140 is chemically inert in a CMP process. In addition, lower portion 140 should be sufficiently elastic that contact of the substrate edge against the retaining ring does not cause the substrate to chip or crack. On the other hand, lower portion 140 should be sufficient rigid to have sufficient lifetime under wear from the polishing pad (on the bottom surface) and substrate (on the inner surface). The plastic of the lower portion 140 can have a durometer measurement of about 80-95 on the Shore D scale. In general, the elastic modulus of the material of lower portion 180 can be in the range of about 0.3-1.0×10⁶ psi. Although the lower portion can have a low wear rate, it is acceptable for the lower portion 140 to be gradually worn away, as this appears to prevent the substrate edge from cutting a deep grove into the inner surface 188.

The first plastic of the lower portion 140 may be (e.g., consist of) polyphenylene sulfide (PPS), polyaryletherketone (PAEK), polyetheretherketone (PEEK) or polyetherketoneketone (PEKK). An advantage of polyphenol sulfide (PPS) is that it is reliable and commonly used material for retaining rings.

The thickness T₁ of lower portion 140 should be larger than the thickness T_(S) of substrate 10. Specifically, the lower portion should be thick enough that the substrate does not contact the adhesive layer when the substrate 10 is chucked by the carrier head. On the other hand, if the lower portion is too thick, the bottom surface of the retaining ring 110 will be subject to deformation due to the flexible nature of the lower portion. The initial thickness of lower portion 140 may be about 50 to 1000 mils, e.g., 100 to 400 mils, depending on the needs of the manufacture and the desired replacement frequency. The lower portion may be replaced when the channels 130 have been worn. The inner surface 116 of the lower portion 140 of the retaining ring can have an inner diameter D (see FIG. 2B) just larger than the substrate diameter, e.g., about 1-2 mm larger than the substrate diameter, so as to accommodate positioning tolerances of the substrate loading system. The retaining ring 110 can have a radial width of about half an inch.

As described above, the bottom surface 114 of the lower portion 180 may be substantially flat, or it may have a plurality of channels 136. The channels 130 extend partially, but not entirely, through the lower portion 180.

The upper portion 142 of the retaining ring 110 is formed of a second plastic that is about equal or greater in rigidity. An advantage of having the second plastic be harder than the first plastic is that the overall rigidity of the retaining ring 110 can be increased, thus reducing deformation of the lower portion 140 when the retaining ring is attached to the carrier head 100, and reducing break-in time. However, it would be acceptable for the second plastic to be slightly softer than the first plastic, e.g., down to 75 or 70 on the Shore D scale, but not significantly softer than the first plastic, or else the retaining ring would become too flexible. The elastic modulus of the material of lower portion 180 can be in the range of about 0.25-50×10⁶ psi. In some implementations, e.g., if carbon fibers are added to the plastic of the upper portion 142 to increase rigidity, the upper portion can have an elastic modulus comparable or greater than stainless steel, e.g., material, an elastic modulus of about 10-50×10⁶ psi, i.e., about ten to one hundred times the elastic modulus of the material of the lower portion 140.

In some implementations, the thickness T₂ of upper portion 140 can be less than the initial thickness T₁ of lower portion 142. However, this is not required; a manufacturer could have a retaining ring 110 in which the thickness T₂ of upper portion 140 is equal to or greater than the initial thickness T₁ of lower portion 142. An advantage of the thickness T₂ of upper portion 140 being less than the initial thickness T₁ of lower portion 142 is increased lifetime of the retaining ring.

The second plastic of the upper portion 142 may be (e.g., consist of) polyvinyl chloride (PVC), polypropylene (PP), polycarbonate (PC), polyaryletherketone (PAEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polybutylene terephthalate (PBT), polyoxymethylene (POM), polyethylene terephthalate (PET), perfluoroalkoxy (PFA), polyamideimide (PAI) or polytetrafluoroethylene (PTFE), or a combination of such materials. In addition, the upper portion 142 can be a composite material such that includes one or more of the above materials as well as carbon fibers to increase the rigidity of the material. In general, the second plastic can be a less expensive material than the first plastic, thus reducing overall cost of the retaining ring 110.

The upper surface 112 of the upper portion 142 can include a plurality of threaded receiving recesses 139. In some implementations, the threaded receiving recesses 139 extend partially, but not entirely through the upper portion 142. However, in some implementations, the threaded receiving recesses 139 extend entirely through the upper portion 142 and into the lower portion 140. The threaded receiving recesses 139 can be spaced apart at equal angular intervals about the retaining ring 110. The threads of the receiving recesses 139 could be machined directly from the second plastic material of the upper portion 142, or could be provided by screw sheaths inserted into holes.

An adhesive layer 144 can be used to secure the upper portion 140 to the lower portion 142. The bonding layer can be made of an adhesive material, such as a slow-curing curing or a fast-curing epoxy. High temperature epoxy resists degradation of the bonding layer 236 due to high heat during the polishing process. In certain implementations, the epoxy includes polyamide and aliphatic amines.

Alternately, instead of being adhesively attached, the upper portion 140 and the lower portion 142 can be connected with screws (e.g., that extend through an aperture in the upper portion 140 into a receiving threaded recess or screw sheath in the lower portion 142), press-fit together, or joined by sonic molding.

When the upper and lower portions 142, 140 of the retaining ring 110 are joined, the upper surface of the lower portion 140 is positioned adjacent to the lower surface of the upper portion 142. The two portions generally have substantially the same dimensions at the inner and outer diameters on their adjacent surfaces such that the upper and lower portions 142, 140 form a flush surface where they meet when they are joined.

Although the retaining ring 110 can include channels 130 for slurry transport in bottom surface 114 of the lower portion 140, and there can be recesses in the top surface of the lower portion 140 to assist in securing of the lower portion 140 to the upper portion 142, the lower portion 140 lacks any aperture that extends from the top surface to the bottom surface of the lower portion.

In some implementations, the retaining ring 110 has one or more through holes that extend horizontally or at a small angle from horizontal through the body of the retaining ring from the inner diameter to the outer diameter for allowing fluid, e.g., air or water, to pass from the interior to the exterior, or from the exterior to the interior, of the retaining ring during polishing. The through-holes can extend through the upper portion 142. The through holes can be evenly spaced around the retaining ring.

Although the side walls of the retaining ring 110 are illustrated as purely vertical, the retaining ring 110 can include other features, such as a lip or recess on the outer surface to assist in centering the retaining ring in a substrate loader or to provide a hard stop for the retaining ring against the top inner edge of a surrounding ring, and the inner or outer surface of the retaining ring 110 can be slightly tapered (although the upper and lower portions 142, 140 can still form a flush surface where they meet).

The present invention has been described in terms of a number of embodiments. The invention, however, is not limited to the embodiments depicted and described. Rather, the scope of the invention is defined by the appended claims. 

1. A retaining ring, comprising: a generally annular lower portion having a bottom surface for contacting a polishing pad during polishing and a top surface, wherein the lower portion is a first plastic; and a generally annular upper portion having a bottom surface secured to the top surface of the lower portion and a top surface configured to be mechanically affixed to and abut a rigid base of a carrier head, wherein the upper portion is a different second plastic that is about the same or more rigid than the first plastic.
 2. The retaining ring of claim 1, wherein the lower portion is secured to the upper portion and the top surface is configured such that the retaining ring is removable as a unit from the base so that the upper portion remains secured to the lower portion while the retaining ring is removed.
 3. The retaining ring of claim 1, wherein the lower portion lacks any aperture from the top surface to the bottom surface of the lower portion.
 4. The retaining ring of claim 1, wherein the lower portion is attached to the upper portion by an adhesive.
 5. The retaining ring of claim 4, wherein the adhesive is an epoxy.
 6. The retaining ring of claim 1, wherein the lower portion has a durometer measurement between about 80 and 95 on the Shore D scale.
 7. The retaining ring of claim 6, wherein the upper portion has a durometer measurement of at least 70 on the Shore D scale.
 8. The retaining ring of claim 7, wherein the upper portion has a greater elastic modulus than the lower portion.
 9. The retaining ring of claim 1, wherein the lower portion is thicker than the upper portion.
 10. The retaining ring of claim 1, wherein the first plastic is selected from the group consisting of polyphenylene sulfide (PPS), polyaryletherketone (PAEK), polyetheretherketone (PEEK) and polyetherketoneketone (PEKK).
 11. The retaining ring of claim 10, wherein the first plastic is polyphenylene sulfide.
 12. The retaining ring of claim 1, wherein the second plastic is selected from the group consisting of polyvinyl chloride (PVC), polypropylene (PP), polycarbonate (PC), polyaryletherketone (PAEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polybutylene terephthalate (PBT), polyoxymethylene (POM), polyethylene terephthalate (PET), perfluoroalkoxy (PFA), polyamideimide (PAI) or polytetrafluoroethylene (PTFE).
 13. The retaining ring of claim 12, wherein the second plastic is polyvinyl chloride.
 14. The retaining ring of claim 1, wherein the bottom surface of the lower portion has channels for slurry transport.
 15. The retaining ring of claim 1, wherein the retaining ring has an inner side wall and an outer side wall, and the inner side wall and outer side wall are oriented vertically from the top surface of the upper portion to the bottom surface of the lower portion.
 16. The retaining ring of claim 1, wherein the inner surface and outer surface of the lower portion and upper portion are flush where the lower portion and upper portion are joined.
 17. The retaining ring of claim 1, wherein the top surface of the upper portion includes a hole to receive a fastener to mechanically affix the retaining ring to the base. 